It is also possible to just remove this from your layout.master
<portal:SiteTitle id="SiteTitle" runat="server"></portal:SiteTitle>
Another tip, once you have made CSS changes, while you can clear your own browser cache you cannot clear the cache for your visitors, so once you complete your css changes the best thing to do is make a new skin folder yourskin_versionx, copy the files into the new skin folder and then change the site to use the new skin. This way the url for the CSS will change and all browsers will load the new CSS whereas if the url does not change the browser may use the copy from cache.
This only applies to CSS since CSS is cahced by the browser, changes made in layout.master are always immediate.
Hope it helps,